1. Field of the Invention
The present invention relates to methods and apparatus for use in electrocardiography.
2. Description of the Prior Art
Present day electrocardiography is performed primarily either by analysis of a spatial vector in which the voltage generated by the heart in one axis is observed in relation to the simultaneous voltage generated in the perpendicular axis, such procedure being known as vectorcardiography, or by analysis of the recorded voltage versus time generated at several points on the surface of the patient's body, such approach being conventionally known as electrocardiogram or ECG. The latter is a method in routine use clinically. The various sites in the body utilized for such electrocardiogram recording, the terminology, and the connections utilized have been standardized by the American Heart Association, such as enumerated in the Report of the Committee on Electrocardiography of the American Heart Association, Circulation 10: 564, 1954, entitled "Recommendations for Standardization of Electrocardiographic and Vectorcardiographic Leads", by Kossman, et al or in another such report, Circulation 35: 583, 1967 entitled "Recommendations for Standardization of Leads and Specifications for Instruments in Electrocardiography and Vectorcardiography", by Kossman et al, and all electrocardiographic machines in the United States rely on such recording techniques. In such conventional standardized systems, in the frontal plane, which is the plane parallel to the body, electrodes are placed on the left arm, generally represented by the letter L, the right arm generally represented by the letter R, and the left leg, generally represented by the letter F, and usually the right leg for a ground, these leads being known as the Einthoven leads which are bipolar leads. Lead I of the Einthoven leads represents the voltage or potential difference between the left arm and the right arm and is represented by the expression L--R; lead II of the Einthoven leads provides the voltage or potential difference between the left leg and the right arm and is represented by the expression F-R; and lead III of the Einthoven leads provides the voltage or potential difference between the left leg and the left arm and is represented by the expression F-L. In addition, in certain prior art electrocardiographic systems, unipolar augmented V leads, such as the type described by Goldberger in a text entitled "Unipolar Lead Electrocardiography", published in Philadelphia in 1949, Second Edition, are utilized as follows: lead AVL, which provides the voltage or potential difference between the left arm and a central terminal as illustrated in FIGS. 14 through 16, where the central terminal is represented by the symbol CT and this potential difference is represented by the expression L-CT; the lead AVR, which provides the voltage or potential difference between the right arm and the central terminal is represented by the expression R-CT; and the lead AVL, which provides the voltage or potential difference between the left leg and the central terminal and is represented by the expression F-CT. An electrocardiogram utilizing the bipolar aand unipolar leads is conventionally provided such as in a typical instrument utilizing a Beckman Type R Dynograph utilizing a No. 9855 Electrocardiogram Input Coupler. These various lead systems, which are conventional, are described in several cardiology textbooks, such as a text entitled "Electrocardiography and Vectorcardiography" by Lamb, published in Philadelphia in 1965, and another textbook entitled "Clinical and Vector Electrocardiography", by Massie and Walsh, published in Chicago, in 1960. In the frontal plane, the six conventionally utilized leads, I, II, III, AVF, AVR and AVL, theoretically fit into an angular relationship which is commonly termed the hexaxial reference system and which is in common usage as a basis for interpreting electrocardiograms and is thoroughly described in the afore-mentioned cardiology textbooks. The lead in which electrocardiogram or ECG changes occur is of great diagnostic value in interpreting the cardiac disease process present, the interpretation of electrocardiograms being dependent on the particular lead in which changes occur. The hexaxial reference system which has been developed has been of assistance in diagnosis and in understanding of the inter-relationships of the various lead systems. However, as presently recorded in conventional electrocardiograms, the angular equivalent of the leads are 0.degree., 60.degree., 120.degree., - 150.degree., - 30.degree., and 90.degree. representing respectively leads I, II, III, AVR, AVL and AVF, which are displayed in that order. Any other angular representations must be imagined by utilizing mental gymnastics. These mental gymnastics are necessarily required in determining the mean vector which has become an important diagnostic determinant for many forms of heart disease, the diagnosis of a particular disease being dependent on the angle of the mean vector. This mean vector angle is normally determined most quickly by observing the lead at which the least forces are developed, each lead representing the electrical force generated by the heart as viewed from a particular selected and specified angle in relation to the site of force generation. The mean vector is recognized as being perpendicular to this lead. Thus, a certain amount of mental gymnastics for each interpretation is required because of the type of display conventionally provided by electrocardiograms. Efforts have been made to minimize the mental gymnastics involved, such as by utilizing complex electronic systems to provide the mean vector as an output of the system, such as described in U.S. Pat. No. 3,548,813 or, as an aid in determining this mean vector, spatial vectometers, such as described in U.S. Pat. No. 2,714,380 have been developed. However these prior art systems have not become widely accepted and mental gymnastics is still required in interpreting present day electrocardiograms. In addition, prior art conventional cardiograms are not satisfactorily readily interpretable for certain types of myocardial infarctions such as posterior myocardial infarctions.